Humus, organic matter which is more or less decomposed anaerobically, has long been recognized as a valuable agricultural material. It is formed on the floors of forests from decomposed leaves and other detritus, in soils where agricultural residues are plowed under, on the bottoms of ponds and lakes from organic matter that has grown therein or falls in; it occurs in peat bogs, in lignite deposits and many other types of minerals and soils, such as Leonardite and Aguja. When any of these materials is treated with alkali, an organic fraction called humic substance dissolves. If the resulting solution is acidified to pH 2 to 3, some of the organic matter precipitates; this material is called humic acid, and the portion which remains in solution is called fulvic acid. Humic substance, then, includes both humic and fulvic acids. The former are complex aggregates, with molecular weights commonly in excess of 1000; the latter have lower molecular weights, of the order of several hundred. either are precise compounds, and thus they are defined by the solubility relations given above.
The properties of humic substance are well-known, and have been applied to the laboratory recovery thereof in the form of humic acid and humate salts from all of the humus materials noted above. On a commercial scale, only humus materials free of cellulosic residues, such as lignite, Leonardite and Aguja, have been employed as a source from which humic substance has been recovered. For example, U.S. Pat. No. 2,992,093 describes a process for the alkaline extraction of humic substance from humus materials, preferably Aguja (a soil said to contain 10-45% of humic substance). Also, U.S. Pat. No. 3,398,186 proposes an alkaline salt extraction of lignite or oxidized coal to recover humic substance. Neither of these patents deals with two major practical problems: Firstly, in such humus materials much of the humic acid is present as sparingly soluble salts which must first be hydrolized by acid before they can be solublized to realize the yield potential of the source; and secondly, these processes are completely impractical where the source contains cellulosic residues, as these swell greatly in alkaline medium, making separations very difficult and yields uneconomically low. The only known commercial attempts to produce these materials have been on sources like Aguja, lignite and Leonardite, which are free of cellulosic residues so that the second problem does not exist. None of these processes have been economically successful because of high processing costs and reduced yields associated with the first problem.
A common, cheap and high-yielding source of humic substance, peat, is subject to both problems, and presently there is no commercial production of humic substance in a purified state from this source. In addition, a third cause of failure to realize economic yields of humic substance by the use of prior known processes is the fact that dried humus material has been used as a starting material. Upon drying, the humic fraction of peat loses much of its ability to dissolve and disperse in water, and consequently the desired product, humic substance, is recovered only with added cost and reduced yield.
The significance of the failure of the prior known processes to provide economical supplies of humic substance and its derivatives is great, because the properties of these materials have long been recognized as giving them substantial agricultural value. In addition, a number of non-agricultural uses for humic substance have been found as a result of laboratory work. These applications have not been developed due to the lack of an economic supply of humic substance and its derivatives.